Italy's largest oil and gas company claimed 77.42 percent of U.K. Burren Energy, emphasizing its $3.5 billion takeover bid, MarketWatch reported.

Eni said the offer is unconditional with regard to acceptances and has lowered the acceptance condition of the offer to 50 percent from 90 percent of the voting rights attached to Burren's issued share capital.

Eni originally agreed to buy Burren in November but the offer was rejected. Eni has paid more than $9.5 billion over the last year, acquiring assets in Congo, Angola, the United States and Russia.

"Burren shareholders who have not yet accepted the offer are urged to do so as soon as possible," Eni officials said.